Loudspeaker system

ABSTRACT

The outer peripheral site of a loudspeaker unit is provided with predetermined air passages formed along substantially the overall inner perimeter of an opening in a baffle plate for allowing a communication between the interior and the exterior of an enclosure, whereby there is provided a loudspeaker system capable of achieving, e.g., improvements in low-frequency characteristics and in transient characteristics while implementing reductions in size and weight. 
     A loudspeaker unit is mounted on the baffle plate in such a manner that between the rear face of the outer peripheral portion of the loudspeaker unit and the front face of the baffle plate there are formed gaps acting as predetermined air passages which extend along substantially overall inner perimeter of the opening in the baffle plate and which allow a communication between the interior and exterior of the enclosure, with an annular rim being provided for regulating the areas confronting both the rear face or the front face of the outer peripheral portion of the loudspeaker unit and the front face or the rear face of the baffle plate, whereby a loudspeaker system is provided which is capable of achieving, e.g., an enhancement in low-frequency characteristics, and an improvement in the quality of sounds over the full frequency range.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a loudspeaker system, andmore particularly to a technique directed at improving the quality ofsounds.

2. Brief Description of the Prior Art

In the conventional loudspeaker systems, importance is commonly attachedto the enclosure sealing properties.

The reason is that any sound pressure leakage from the enclosure mayadversely affect the frequency characteristics.

More specifically, sound waves leaking from the enclosure may interferewith direct sounds from the loudspeaker system and disturb the frequencycharacteristics. In particular, sound waves leaking from the site apartfarther from the loudspeaker system may often have the same soundpressure phases within the interior of the enclosure, resulting in anacute interference.

It is therefore an inviolable rule in typical mounting of theloudspeaker unit on the enclosure baffle to keep the sealing at themounting surfaces. This mounting is carried out in a textbook manner.

As can be seen in FIGS. 25(A) and 25(B) for example, a loudspeaker unit1 is mounted such that the internal face of a flange portion 2 at itsperipheral portion comes into intimate contact with the front face of abaffle plate 4 of an enclosure 3. Alternatively, the loudspeaker unit 1is mounted such that the external face of the flange portion 2 comesinto intimate contact with the rear face of the baffle plate 4.

In general, the bass characteristics of the loudspeaker system arerestricted by the lowest resonance frequency of the loudspeaker unit andthe requirement for reproduction of the unit lowest resonance frequencyis to impart a sufficient capacity to the unit mounted enclosure. In theconventional loudspeaker systems attaching importance to the enclosuresealing properties, however, the action on the diaphragm of inertialvibrations of the air spring within the enclosure may adversely affectthe low-frequency characteristics and transient characteristics of theloud speaker system. In particular, if the mounting capacity is smallerthan the enclosure capacity required by the loudspeaker unit, then thelow-frequency characteristics may suffer a remarkable damping.

A loudspeaker unit having a large-diameter diaphragm is suitable for thebass reproduction although use of the large-diameter diaphragm may leadto an increase of the enclosure capacity, rendering an enlargement indimensions of the loudspeaker system inevitable.

For this reason, the typical loudspeaker system intended for the bassreproduction is apt to add to its size and weight, resulting in highcosts and low handling properties.

With a view to solving such deficiencies and reducing the system size,there have been proposed a system using bass reflex, a resonance chamberor an acoustic tube for loading, a seal-up system having soundabsorption materials filled into the interior thereof, and a systemmaking corrections based on output detection such as motional feedbackand including an electronic circuit such as an equalizer. All of themhave however caused any complications instructure, resulting inevitablyin arise of fabrication costs. In such cases, the systems had tendenciesof the quality of sounds proper thereto.

Hitherto known as the loudspeaker system cabinet (enclosure) is an R-Jcabinet of a type in which as illustrated in FIG. 26 a loudspeaker unit5 fitted to a supplementary baffle plate 6 is mounted on a baffle plate8 at the front of a cabinet (enclosure) 7 in a spaced apart manner.

In this R-J cabinet, however, air passages allowing a communicationbetween the interior and exterior of the cabinet 7 open to opposed sideends of an opening 9 of the baffle plate 8, with the result that inspite of its improved bass characteristics the output sound pressurelevels in the mid-frequency band will lower with its characteristicshaving peaks in the vicinity of the bass reproduction limit frequency.

In the past, there has also been proposed a configuration in which apartition is positioned behind the diaphragm spaced by a predetermineddistance apart from the diaphragm so as to define an acoustic spacetherebetween, the inner periphery of the acoustic space leading into thespace within the loudspeaker box, the outer periphery of the acousticspace opening to the front face of the loudspeaker box by way of an airvent ring (see Japanese Patent Laid-open Pub. No. Hei2-195796).

This configuration allows the space defined between the partition andthe diaphragm to act as a duct for effectively guiding the bassreproduction outputs of the loudspeaker and to enhance the basses sincethe space at its inner periphery leads into the space within theloudspeaker box and at its outer periphery opens to the front face ofthe loudspeaker box.

It is however difficult to readily apply this technique to the existingloudspeaker system because the loudspeaker unit itself needs to have anunique specification due to its configuration in which the partition andthe air vent ring are integrally mounted on the diaphragm, i.e., thecone to make up the loudspeaker system thereby forming the above spaceportion.

At the same time, the structure of the cone is also complicated with itsincreased weight, disadvantageously adding to costs.

Furthermore, due to its bent configuration of the space portion, asmooth radiation of air within the enclosure is not achieved, renderingit difficult to effectively prevent any influence on the diaphragm ofthe inertial vibrations of the air spring within the interior of theenclosure.

SUMMARY OF THE INVENTION

The present invention was conceived in order to solve the conventionalproblems as set forth hereinabove. It is therefore the object of thepresent invention to provide a simple improved attachment structure tothe baffle plate of the enclosure of the loudspeaker unit to therebyachieve a reduction in size and weight of the loudspeaker system andachieve an enhancement in the low-frequency characteristics andtransient characteristics.

In addition to the above object, it is another object to ensure an easyand secure adjustment of the gaps formed along substantially the overallinner perimeter of the opening in the baffle plate between the rear faceof the outer peripheral portion of the loudspeaker unit and the frontface of the baffle plate, to thereby achieve an enhancement in the basscharacteristics and an improvement in the quality of sounds forinstance.

The loudspeaker system according to a first aspect of the presentinvention can satisfy items (1) to (4) which follow.

(1) To enhance the low-frequency band through radiation of resonantsounds within the interior of the enclosure.

(2) To improve the transient characteristics over the full reproductionrange to acquire a free, easy and gloomless quality of sounds throughthe reduction of influences on the diaphragm of inertial vibrations ofair springs within the interior of the enclosure.

(3) To achieve more effectively an improvement in the quality of soundthrough effective reduction of resistance to which the coned paper issubjected as a result of a variation in the air pressure within theinterior of the enclosure.

(4) To enhance the bass frequency characteristics and simultaneouslyprevent any turbulence of characteristics at the other frequencies.

To this end, according to the first aspect of the present invention,there is provided a loudspeaker system including an enclosure and aloudspeaker unit adapted to be fitted to an opening in a baffle plate atthe front of the enclosure, wherein around the outer peripheral site ofthe loudspeaker unit there are formed predetermined air passages whichextend along substantially the overall inner perimeter of the opening inthe baffle plate, for allowing a communication between the interior andexterior of the enclosure.

It has been found out that in the woofer unit or full-range unit, theoptimal value can be conferred on the spatial volume providedequi-angularly between the periphery of the woofer unit frame and thebaffle face by use of the spacers at the positions of the unit mountingscrews, whereby the optimal spatial volume can serve as a regulator tocontrol the air pressure within the enclosure. Furthermore, the qualityof sounds from the sound generator has been improved by fixing thevibration body to the baffle face at several points in place of thesurfaces.

The predetermined air passages allowing a communication between theinterior and exterior of the enclosure serve as sound holes whichthrough the bass reflex action radiate resonant sounds within theinterior of the enclosure to reinforce the bass frequencies.

Influences on the diaphragm of inertial vibrations of the air springlying within the enclosure are reduced and transient characteristicsover the full reproduction range are improved, with the result that afree, easy and gloomless sound quality is obtained.

Furthermore, since the air passages are formed along the outerperipheral site of the loudspeaker unit so as to extend alongsubstantially the overall inner perimeter of the opening in the baffleplate, air can flow in and out uniformly through the outer peripheralsite of the loudspeaker unit and the coned paper of the loudspeaker unitcan have a gentle curvature toward the air passages, with the resultthat resistance to which the coned paper may be subjected as a result ofa variation in the air pressure within the interior of the enclosure iseffectively reduced, achieving an effective improvement in the qualityof sounds.

In particular, since the air passages are formed in close vicinity tothe loudspeaker unit and along substantially the overall inner perimeterof the opening in the baffle plate, it is possible to enhance the bassfrequency characteristics as well as to prevent any turbulences ofcharacteristics at the other frequencies.

In such a case, the loudspeaker unit may be mounted on the baffle platein such a manner that gaps are defined as the air passages between therear face of the outer peripheral portion of the loudspeaker unit andthe front face of the baffle plate.

Alternatively, the loudspeaker unit may be mounted on the baffle platein such a manner that gaps are defined as the air passages between thefront face of the outer peripheral portion of the loudspeaker unit andthe rear face of the baffle plate.

In this case, by way of a plurality of spacers, the gaps may be formedbetween the internal face of the outer peripheral portion of theloudspeaker unit and the front face of the baffle plate or between theexternal face of the outer peripheral portion of the loudspeaker unitand the rear face of the baffle plate.

The plurality of spacers may each be in the form of a substantiallytubular member, with fittings inserted through the interior of thetubular member being securely fastened to the outer peripheral portionof the loudspeaker unit and to the baffle plate.

In this event, preferably the plurality of spacers are each formed of amaterial having a predetermined vibration absorptivity.

The plurality of spacers may be formed integrally with the loudspeakerunit or with the baffle plate.

In case of the configuration where the loudspeaker unit is mounted onthe baffle plate in such a manner that the gaps are formed as the airpassages between the rear face of the peripheral portion of theloudspeaker unit and the front face of the baffle plate, the enclosuremay have a top wall portion and a bottom wall portion which are extendedforwardly, the enclosure having a pair of right and left support memberssituated in front of the baffle plate for coupling to the extendedportions, with the outer peripheral portion of the loudspeaker unitbeing fitted to the support members so as to space the outer peripheralportion of the loudspeaker unit apart from the baffle plate, to therebyform the gaps.

Furthermore, the loudspeaker unit may have an attachment protrusionformed integrally with its outer peripheral portion, the attachmentprotrusion having a plurality of openings which provide the airpassages, the attachment protrusion being fitted to the external face orinternal face of the baffle plate.

Also, the baffle plate may have an attachment protrusion projecting fromthe inner peripheral face of the opening, the loudspeaker unit having anattachment protrusion which projects from its outer peripheral face, twothe attachment protrusions being coupled together so as to form gapsacting as the air passages between the inner peripheral face of theopening and the outer peripheral portion of the loudspeaker unit.

Incidentally, the enclosure may have a bass reflex port or a bassradiation hole for bass reflex.

In case of the provision of such a bass reflex port by the bass reflexduct or the provision of the bass radiation hole for bass reflex, theperipheral sound pressure can be raised by employing as low a resonancefrequency as possible of the bass reflex port or the bass radiationhole.

The loudspeaker system according to a second aspect of the presentinvention can satisfy items (1) to (4) which follow.

(1) To achieve a reduction in size and weight of the enclosure whilesimultaneously ensuring an enhanced low-frequency band, a low distortionand a high efficiency.

(2) To provide a loudspeaker system having improved transientcharacteristics and economic considerations.

(3) To restrain a reduction of the additional mass on the loudspeakerunit diaphragm which may arise from air within the interior of theenclosure, to thereby suppress the damping in the bass reproductioncharacteristics.

(4) To secure effectiveness in any small-sized loudspeaker systems whichare liable to undergo a reduction in the addition mass on theloudspeaker unit diaphragm and which are apt to suffer any damping inthe bass reproduction characteristics.

To this end, according to the second aspect of the present invention,there is provided a loudspeaker system including an enclosure and aloudspeaker unit adapted to be fitted to an opening in a baffle plate atthe front of the enclosure, wherein the loudspeaker unit is mounted onthe baffle plate in such a manner that between the rear face of theouter peripheral portion of the loudspeaker unit and the front face ofthe baffle plate there are formed gaps acting as predetermined airpassages which extend along substantially the overall inner perimeter ofthe opening in the baffle plate and which allow a communication betweenthe interior and exterior of the enclosure, and wherein said loudspeakerunit has on its outer peripheral portion rear face an annular rim foradjusting confronting areas of the rear face of said outer peripheralportion and of the front face of said baffle plate.

Alternatively, there is also provided a loudspeaker system including anenclosure and a loudspeaker unit adapted to be fitted to an opening in abaffle plate at the front of the enclosure, wherein the loudspeaker unitis mounted on the baffle plate in such a manner that between the frontface of the outer peripheral portion of the loudspeaker unit and therear face of the baffle plate there are formed gaps acting aspredetermined air passages which extend along substantially the overallinner perimeter of the opening in the baffle plate and which allow acommunication between the interior and exterior of the enclosure, andwherein the loudspeaker unit has on its outer peripheral portion frontface an annular rim for adjusting confronting areas of the front face ofthe outer peripheral portion and of the rear face of the baffle plate.

It has been found out that in the woofer unit or full-range unit, theoptimal value can be conferred on the spatial volume providedequi-angularly between the periphery of the woofer unit frame and thebaffle face by use of the spacers at the positions of the unit mountingscrews, whereby the optimal spatial volume can serve as a regulator tocontrol the air pressure within the enclosure. Furthermore, the qualityof sounds from the sound generator has been improved by fixing thevibration body to the baffle face at several points in place of thesurfaces.

The predetermined air passages allowing a communication between theinterior and exterior of the enclosure serve as sound holes whichthrough the bass reflex action radiate resonant sounds within theinterior of the enclosure to reinforce the bass frequencies.

Influences on the diaphragm of inertial vibrations of the air springlying within the enclosure are reduced and transient characteristicsover the full reproduction range are improved, with the result that afree, easy and gloomless sound quality is obtained.

Furthermore, since the air passages are formed along the outerperipheral site of the loudspeaker unit so as to extend alongsubstantially the overall inner perimeter of the opening in the baffleplate, air can flow in and out uniformly through the outer peripheralsite of the loudspeaker unit and the coned paper of the loudspeaker unitcan have a gentle curvature toward the air passages, with the resultthat resistance to which the coned paper may be subjected as a result ofa variation in the air pressure within the interior of the enclosure iseffectively reduced, achieving an effective improvement in the qualityof sounds.

Also, since the air passages are formed in close vicinity to theloudspeaker unit and along substantially the overall inner perimeter ofthe opening in the baffle plate, it is possible to enhance the bassfrequency characteristics as well as to prevent any turbulences ofcharacteristics at the other frequencies.

Then, for a bass loudspeaker including a flame rib which acts as thefitting surface to the baffle plate but has no even annular shape orincluding a small fitting surface area wherein it may be difficult toregulate the gaps formed along substantially the overall inner perimeterof the baffle plate opening between the rear face of the outerperipheral portion of the loudspeaker unit and the front face of thebaffle plate, a large-diameter annular rim is mounted on the front faceor rear face of the outer peripheral portion of the loudspeaker unit soas to increase the confronting areas of the rear face or front face ofthe outer peripheral portion and of the front face or rear face of thebaffle plate, whereby there can easily be achieved an enhancement in thelow-frequency characteristics and an improvement in the quality ofsounds over the full range.

In the mid-frequency sound loudspeaker system and the high-frequencysound loudspeaker system, for the purpose of improving the auditorylocalization of image sounds through the radiation of sounds within theenclosure from the periphery thereof, a large-diameter annular rim ismounted on the rear face or front face of the outer peripheral portionof the loudspeaker unit so as to increase the confronting areas of boththe rear face or the front face of the outer peripheral portion of theloudspeaker unit and the front face or the rear face of the baffleplate, thereby making it possible to prevent the low-frequencycharacteristics from being degraded.

In such a case, in the configuration where the annular rim is providedon the rear face of the outer peripheral portion of the loudspeakerunit, the loudspeaker unit may have on its outer peripheral portion anannular rim portion located at the rear face of the outer peripheralportion, a plurality of spacer portions projecting backward from therear face of the annular rim portion, and a ring-like rib portionpositioned behind the rear face of the annular rim portion for couplingthe plurality of spacers to one another, the rim portion, the pluralityof spacer portions and the rib portion being integrally formed with theouter peripheral portion of the loudspeaker unit, the rib portion beingfitted to the front face of the baffle plate.

In case of providing the annular rim on the external peripheral portionfront face of the loudspeaker unit, the loudspeaker unit may have on itsouter peripheral portion an annular rim portion located at the frontface of the outer peripheral portion, a plurality of spacer portionsprojecting forward from the front face of the annular rim portion, and aring-like rib portion positioned in front of the front face of theannular rim portion for coupling the plurality of spacers to oneanother, the rim portion, the plurality of spacer portions and the ribportion being integrally formed with the outer peripheral portion of theloudspeaker unit, the rib portion being fitted to the rear face of thebaffle plate.

By virtue of the structure where the annular rim and spacers arepreviously formed integrally with the loudspeaker unit itself in thismanner, the number of parts of the apparatus can totally be reduced.Application of the present invention to any loudspeaker systems willthus become possible by the attachment of only the loudspeaker unit,contributing to fabrication easiness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a first embodiment of aloudspeaker system in accordance with a first aspect of the presentinvention.

FIG. 2 is a longitudinal sectional view of a second embodiment.

FIG. 3 is a perspective view for explaining a method of fastening abaffle plate, spacers and a loudspeaker unit together by means ofmachine screws.

FIGS. 4(A) and 4(B) are a perspective view and a sectional view,respectively, showing a variant of the first embodiment.

FIG. 5 is a longitudinal sectional view showing another variant of thefirst embodiment.

FIGS. 6(A) and 6(B) are perspective views of third and fourthembodiments, respectively.

FIG. 7 is a perspective view of a fifth embodiment.

FIG. 8 is a perspective view of a sixth embodiment.

FIG. 9 is a perspective view of a seventh embodiment.

FIGS. 10(A) and 10(B) are front elevational view and a sectional viewtaken along a line A—A of FIG. 10(A), respectively, each showing aneighth embodiment.

FIG. 11 is a graphic representation showing the results of experimentson frequency characteristics of conventional loudspeaker system.

FIG. 12 is a graphic representation showing the results of experimentson frequency characteristics of the loudspeaker system in accordancewith the first aspect of the present invention.

FIG. 13 is a graphic representation showing the results of experimentson frequency characteristics of the loudspeaker system in accordancewith the first aspect of the present invention.

FIG. 14 is a longitudinal sectional view of a first embodiment of aloudspeaker system in accordance with a second aspect of the presentinvention.

FIG. 15 is a longitudinal sectional view of a second embodiment of thesame.

FIGS. 16(A) and 16(B) are a front elevational view and a sideelevational view, respectively, each showing a third embodiment of thesame.

FIG. 17 is a longitudinal sectional view showing a fourth embodiment.

FIG. 18 is a graphic representation showing the results of experimentson frequency characteristics of a conventional loudspeaker system and ofthe loudspeaker system of the present invention.

FIG. 19 is a graphic representation showing the results of experimentson frequency characteristics of the loudspeaker system in accordancewith the second aspect of the present invention.

FIG. 20 is a graphic representation showing the results of experimentson frequency characteristics of the loudspeaker system in accordancewith the second aspect of the present invention.

FIG. 21 is a graphic representation showing the results of experimentson frequency characteristics of the loudspeaker system in accordancewith the second aspect of the present invention.

FIG. 22 is a graphic representation showing the results of experimentson frequency characteristics of the loudspeaker system in accordancewith the second aspect of the present invention.

FIG. 23 is a graphic representation showing the results of experimentson frequency characteristics of the loudspeaker system in accordancewith the second aspect of the present invention.

FIG. 24 is a graphic representation showing the results of experimentson frequency characteristics of the loudspeaker system in accordancewith the second aspect of the present invention.

FIGS. 25(A) and 25(B) are longitudinal sectional views showing theconventional loudspeaker system by way of example.

FIG. 26 is a perspective view of another example of the conventionalloudspeaker system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described here in below.

The present invention will now be described in greater detail withreference to the accompanying drawings.

Description is first made of a first aspect of the present invention.

The basic concept of the first aspect is as follows.

The problems of loudspeaker size reduction and its attendant degradationin bass frequency characteristics can be solved by isolating thediaphragm of the loudspeaker unit from any influence of damping whichmay be caused by the air spring lying within the enclosure.

For example, a stringed instrument such as a guitar or a contrabass canproduce excellent basses or low-frequency sounds under the action of itsresonance box although it merely has vibrating elements with minutesurface areas in the form of strings. It can also produce extremely richharmonics providing overtone components.

This is due to the fact that vibrations of the strings acting as thevibrating elements are transmitted via the bridges to the resonance boxso as to utilize the resonance of the body as much as possible.

As is apparent from this example, the enclosure can be used as theresonance box in order to achieve most simple and effective reproductionof basses by the loudspeaker system.

Thus, according to the basic concept of the first aspect of the presentinvention, the outer peripheral site of the loudspeaker unit is providedwith predetermined air passages extending along substantially theoverall inner perimeter of the baffle plate opening, for allowing acommunication between the interior and exterior of the enclosure, andthe loudspeaker unit is located apart from the opening, e.g., to such anextent as to prevent an occurrence of degradation of bass frequencycharacteristics arising from detouring of the basses without anyintimate contact with the baffle plate opening surface of the enclosure,to thereby obviate any influences on the diaphragm of the air springlying within the enclosure to consequently achieve an effective use ofthe enclosure as the resonance box.

Description will then be made of embodiments of the loudspeaker systembased on such a basic concept of the first aspect of the presentinvention.

FIG. 1 is a longitudinal sectional view of the loudspeaker system inaccordance with a first embodiment.

In this diagram, the loudspeaker system comprises an enclosure 10 and aloudspeaker unit 13 fitted to an opening 12 in a baffle plate 11situated at the front of the enclosure 10.

The loudspeaker unit 13 is mounted on the baffle plate 11 in such amanner that gaps are formed between the rear face of a flange 14 at theouter peripheral portion of the loudspeaker unit 13 and the front faceof the baffle plate 11, the gaps providing predetermined air passagesallowing a communication between the interior and the exterior of theenclosure 10.

In this embodiment, a plurality of tubular spacers 15 are interposedbetween the internal face of the flange 14 at the outer peripheralportion of the loudspeaker unit 13 and the front face of the baffleplate 11 so that the loudspeaker unit 13 is secured to the baffle plate11 by means of machine screws 16 acting as fittings for insertion intothe spacers 15.

In this case, eight screw insertion holes are formed in anequi-angularly spaced manner in both the outer periphery of the flange14 of the loudspeaker unit 13 and the inner perimeter of the opening inthe baffle plate 11, and as illustrated in FIG. 3, the machine screws 16are inserted through the insertion holes associated with the loudspeakerunit 13, through holes of the spacers 15 and through the insertion holesassociated with the baffle plate 11 in the mentioned order, after whichnuts 17 are screwed and tightened onto ends, protruding from the rearface of the baffle plate 11, of threaded leading portions of the machinescrews.

The spacers 15 for use herein can be made of, e.g., a rigid materialsuch as metals (vibration transmission type), or a resilient material ormember such as rubbers or coil springs (vibration absorption type).

It is preferred in case of the vibration absorption spacer 15 thatbetween the nut 17 and the baffle plate 11 there intervene a washer madeof rubber or other resilient material.

FIG. 2 is a longitudinal sectional view of a loudspeaker system inaccordance with a second embodiment.

In this embodiment, the loudspeaker unit 13 is mounted in such a mannerthat between the front face of its flange 14 and the rear face of thebaffle plate 11 there are formed gaps having a predetermined distance.

In this embodiment, the plurality of spacers 15 are interposed betweenthe front face of the loudspeaker unit 13 and the rear face of thebaffle plate 11 so that the loudspeaker unit 13 is fitted to the baffleplate 11 by means of the machine screws 16 inserted through the spacers15.

The spacers 15 may be formed integrally with the loudspeaker unit 13 orwith the baffle plate 11.

For example, as seen in FIGS. 4(A) and 4(B), the baffle plate 11 maypreviously have a plurality of spacer portions 15A formed integrallythere with so that the flange 14 of the loudspeaker unit 13 can beattached to the spacer portions 15A.

For this attachment, as shown in the same diagram, rivets 15B or splitpins can be used. Alternatively, use may be made of pins and C-ringsfitted into the pins.

It will be appreciated that as illustrated in FIG. 5, a recessed portion1A may be formed around the opening 12 on the external face of thebaffle plate 11 so that the flange 14, the spacers 15 and the baffleplate 11 can be fastened together within the interior of the recessedportion 11A, whereby a smart shape is conferred on the loudspeakersystem 10 without any protrusion of the loudspeaker unit 13 from thefront face of the baffle plate 11.

FIGS. 6(A) and 6(B) are perspective views of a loudspeaker unit of aloudspeaker system in accordance with third and fourth embodiments,respectively.

In the embodiment of FIG. 6(A), the flange 14 of the loudspeaker unit 13is provided integrally with a plurality of spacer portions 18 projectingbackward from the rear face of the flange 14 and with a ring-like rib 19positioned behind the rear face of the flange 14 for coupling the spacerportions 18 with one another, the rib 19 being fastened to the baffleplate front face by means of machine screws and nuts.

In the embodiment of FIG. 6(B), the flange 14 of the loudspeaker unit 13is provided integrally with a plurality of spacer portions 20 projectingforwardly from the front face of the flange 14 and with a ring-like rib21 positioned in front of the front face of the flange 14 for couplingthe spacer portions with one another, the rib 21 being fastened to thebaffle plate rear face by means of machine screws and nuts.

FIG. 7 is a perspective view of a loudspeaker unit of a loudspeakersystem in accordance with a fifth embodiment. In this embodiment, aplurality of ribs 22 providing spacers are formed integrally around theopening 12 in the baffle plate 11, the ribs 22 each having a groove 22Aformed in the inner peripheral surface thereof, whereas the flange 14 ofthe loudspeaker unit 13 is provided with a plurality of outwardlyextending fitting protrusions 23, whereby the fitting protrusions 23 canbe fitted into the grooves 22A of the ribs 22 by turning the loudspeakerunit 13.

FIG. 8 is a perspective view of a loudspeaker unit of a loudspeakersystem in accordance with a sixth embodiment. In this embodiment, theenclosure 10 has forwardly extending top and bottom walls to which apair of right and left support members 24 are coupled via theirrespective upper and lower ends, the support members 24 being situatedat the front of the baffle plate 11 so that the flange 14 of theloudspeaker unit 13 is fitted to the pair of support members 24, wherebythe flange 14 of the loudspeaker unit 13 is spaced apart from the baffleplate 11 to form gaps providing air passages between the flange 14 ofthe loudspeaker unit 13 and the opening 12.

FIG. 9 is a perspective view of a loudspeaker unit of a loudspeakersystem in accordance with a seventh embodiment.

In this embodiment, the flange 14 of the loudspeaker unit 13 is providedintegrally with a fitting plate 25 having a plurality of openings 25A,the fitting plate 25 being mounted on the external face or internal faceof the baffle plate.

In this case, the openings 25A provide air vents around the outerperipheral portion of the loudspeaker unit 13.

FIGS. 10(A) and 10(B) are a front elevational view and a sectional view,respectively, of a loudspeaker unit of a loudspeaker system inaccordance with an eighth embodiment.

In this embodiment, a plurality of inwardly extending fittingprotrusions 26 are formed around the inner peripheral surfaces of theopening 12 of the baffle plate 11, whereas a plurality of outwardlyextending fitting protrusions 27 are formed around the outer peripheralsurface of the loudspeaker unit 13 in order that the fitting protrusions27 are fastened to the fitting protrusions 26 by means of machine screws28 or the like.

In this embodiment, gaps are formed as air passages between the innerperipheral surface of the opening 12 and the outer peripheral portion ofthe loudspeaker unit 13.

According to the thus configured loudspeaker system, the outerperipheral site of the loudspeaker unit is provided with predeterminedair passages formed along substantially the overall inner perimeter ofthe opening in the baffle plate, the air passages allowing acommunication between the interior and exterior of the enclosure,whereby the following functions and effects are presented.

That is, the predetermined air passages allowing a communication betweenthe interior and exterior of the enclosure serve as sound holes whichthrough the bass reflex action radiate resonant sounds within theinterior of the enclosure to reinforce the bass frequencies.

Influences on the diaphragm of inertial vibrations of the air springlying within the enclosure are reduced and transient characteristicsover the full reproduction range are improved, with the result that afree, easy and gloomless sound quality is obtained.

Furthermore, since the air passages are formed along the outerperipheral site of the loudspeaker unit so as to extend alongsubstantially the overall inner perimeter of the opening in the baffleplate, air can flow in and out uniformly through the outer peripheralsite of the loudspeaker unit and the coned paper of the loudspeaker unitcan have a gentle curvature toward the air passages, with the resultthat the resistance to which the coned paper may be subjected as aresult of a variation in the air pressure within the interior of theenclosure is effectively reduced, achieving an effective improvement inthe quality of sounds.

In particular, since the air passages are formed in close vicinity tothe loudspeaker unit and along substantially the overall inner perimeterof the opening in the baffle plate, it is possible to enhance the bassfrequency characteristics as well as to prevent any turbulences ofcharacteristics at the other frequencies.

By the way, in cases where the air passages are spaced apart from theloudspeaker unit to a great extent, there is a deficiency that althoughthe bass frequency characteristics can be reinforced, the otherfrequencies may be subjected to any turbulences as set forth inconnection with the prior art.

It has been found out that in the woofer unit or full-range unit, theoptimal value can be conferred on the spatial volume providedequi-angularly between the periphery of the woofer unit frame and thebaffle face by use of the spacers at the positions of the unit mountingscrews, whereby the optimal spatial volume can serve as a regulator tocontrol the air pressure within the enclosure. Furthermore, the qualityof sounds from the sound generator has been improved by fixing thevibration body to the baffle face at several points in place of thesurfaces.

It is thus possible to suppress any damping in the bass characteristicseven when the mounting volume is smaller than the enclosure volumerequired by the loudspeaker unit, whereupon a small-sized enclosure canbe used for the loudspeaker unit having a large-diameter diaphragmcapable of high-efficient and high-withstand input, therebysimultaneously achieving an improvement in efficiency and a reduction insize of the loudspeaker system.

In particular, by forming the gaps acting as air passages with theintervention of a plurality of spacers between the internal face of theouter peripheral portion of the loudspeaker unit and the front face ofthe baffle plate or between the external face of the outer peripheralportion of the loudspeaker unit and the rear face of the baffle plate,the embodiments have the following advantages.

That is, the spacers can transmit vibrations of the loudspeaker unitframes to the baffle plate and act like the bridges of the contrabass,increasing the above resonance through the vibrations of the enclosure.

Also, depending on the design purposes, the spacers can be made ofmaterials such as rubber or other resins having a large vibrationabsorptivity or of materials such as metals having a small vibrationabsorptivity so as to provide a control of the resonance of the baffleplate.

Furthermore, it is possible to form air vents at the outer peripheralportion of the loudspeaker unit by simple modifications such as additionof the spacers, alterations of shape of the opening in the baffle plateand alterations of shape of the outer peripheral portion of theloudspeaker unit, thereby eliminating a need to impart uniquespecifications to the loudspeaker unit itself, allowing an easyapplication to the existing loudspeaker systems, and providingcost-efficient loudspeaker unit structure without causing anycomplication and any increase in weight.

As shown in FIG. 1, in case of providing a bass reflex port by a bassreflex duct 29 or providing a bass radiation hole not shown for bassreflex, it is possible to raise the output sound pressure by employing apossible lowest resonance frequency of the bass reflex port or of thebass radiation hole.

The above embodiments of the first aspect of the present invention areapplicable to loudspeaker systems provided in various types of acousticequipment, especially to loudspeaker systems for SR systems, domesticaudio loudspeaker systems, radio cassette players, sing-along machines,personal computers and television sets.

In the event of the loudspeaker units built into the wall surfaces orautomobile doors in particular, the loudspeaker units can be mounted onthe fitting portion (acting as the baffle plate) in accordance with themethods of the above embodiments.

Furthermore, in order to improve the external appearance, the openingsof the air passages toward the exterior may be covered with asound-permeable cloth or the like.

In case of aiming to reproduce a heavy low-frequency band, it ispossible to effectively extend the bass reproduction limit frequency byfurther adding resonance ducts or adding motional feedback or equalizeroperations to the loudspeaker systems including the loudspeaker unitsconfigured in accordance with the first aspect of the present invention.

The inventors have herein made experiments for comparing the loudspeakersystem of the first aspect based on the following specifications (use ofthe spacers with the bass reflex duct or without the bass reflex duct)with the conventional loudspeaker system based on the abovespecifications (no use of the spacers without the bass reflex duct).

(Loudspeaker System Specifications)

A 38 cm dia. woofer unit (f_(o)=40 Hz) was mounted as the loudspeakerunit on a seal-up enclosure (inner dimensions: 90.8 cm (height)×45.2 cm(width)×44.2 cm (depth)) having an actual volume of 163 lit. (innervolume 181 lit.) in such a manner as to be spaced apart by apredetermined distance Rh from the baffle plate by means of the spacersas in the embodiments of FIGS. 1 and 2 for example.

While hearing musical signals, the spacer length was varied to 5 mm, 10mm, 15 mm and 20 mm and the frequency characteristics and impedancecharacteristics were measured to obtain the optimum value of thepredetermined distance Rh.

Furthermore, in order to improve the ultra-bass characteristics, twobass reflex ducts of e.g., 8 cm×38 cm (vinyl chloride pipe) wereprovided.

In such a case, an opening was formed at the lower portion of the baffleplate, and the pipe duct arranged horizontally within the enclosure wasfixedly mounted in such a manner that its top opening communicates withthe opening.

As a result, a communication was established via the bass reflex ductbetween the interior and the exterior of the enclosure.

In case of the seal-up enclosure, the ideal value of the actual volumeof the 38 cm dia. woofer unit used was 225 lit although its actualvolume was 165 lit. (72.4% of the ideal value) as described above. Theconventional loudspeaker system exhibited a low-frequency characteristicdamping from 150 Hz onward as seen in FIG. 11 since the large-diameterloudspeaker unit having a larger S0 was mounted on the enclosure shortof volume.

Sound qualities lacking low-frequency weightiness and mid-frequencyclearness were thus created, making high fidelity reproduction usedifficult.

The loudspeaker system (using 15 nm spacers without the bass reflexduct) in accordance with the first aspect of the present inventionpresented a substantially flat characteristic till 60 Hz as illustratedin the graph of FIG. 12.

The loudspeaker system (using 10 mm spacers with two 8 cm×38 cm bassreflex ducts (the bass reflex ducts have as large a length as possibleso that they can reach the full depth of the enclosure)) in accordancewith the first aspect of the present invention provided quite a flatfrequency characteristic between 60 Hz to 100 Hz with the bassreproduction limit at 6 db down value being 50 Hz as illustrated in thegraph of FIG. 13.

Thus, this loudspeaker system was able to reproduce sounds of bassinstruments such as contrabasses in jazz or classical music naturallyand in a realistic manner without causing any distortive feelings, indistinctness or exaggerations. At the same time, remarkably improvedwere tones of high-frequency noise components which may occur whenplucking strings characteristic of pizzicato or electric bass glissando.

It has also turned out that by the combination of the loudspeaker unithaving a small stiffness S₀ and having a large effective vibrationalmass M₀ and the configuration of the first aspect of the presentinvention (using the spacers), a further reduction in system dimensions(about 30% reduction at the enclosure volume ratio upon the use of thecurrent loudspeaker unit of the same type) can easily be achieved atlower costs without degrading any bass characteristics.

In the above, description has been made of the 38 cm dia. loudspeakerunit. Then, while hearing musical signals, the frequency characteristicsand impedance characteristics were measured to obtain optimal values ofthe predetermined distance Rh from the baffle plate in the loudspeakerunits having the other diameters (e.g., of 30 cm).

Furthermore, the inventors has done experiments (1) to (3) which follow.

(1) For a small diameter loudspeaker unit, air vents were formed in theenclosure by use of spacers to examine the quality of sounds.

(2) For a middle diameter loudspeaker unit of the order of 20 cm dia.,air vents were formed in the enclosure by use of spacers to examine thequality of sounds.

The spacers for use in this case were each in the shape of a washer ofthe order of 1 mm thick.

The results of those experiments revealed that five-degree lower tonesin the musical scale notation can be reproduced as well as enhancedfeelings of separation of instruments, depths and real existences.

In the event that the volume of the enclosure is reduced toone-several-th of V_(as) of the loudspeaker unit, it is preferred thatthe interior of the enclosure be filled with an acoustic material inorder to reduce the internal impedance of the enclosure.

In this case, rather than the effect of resonance of the enclosure, aneffect is especially expected that there may be reduced the influence onthe diaphragm of the inertial vibrations of the air spring lying withinthe enclosure.

(3) For a three-way loudspeaker system having separate loudspeaker unitsfor low-frequency sounds, mid-frequency sounds and high-frequencysounds, air vents were formed in the enclosure by use of the spacers toexamine the quality of sounds.

According to the results of this experiment, any improvement in thequality of sounds has been found out in all of the loudspeaker units forlow-frequency sounds, mid-frequency sounds and high-frequency sounds.

That is, the first aspect of the present invention contributes toimprovements in the quality of sounds not merely in the low-frequencysound loudspeaker unit but also in the middle and high-frequency soundloudspeaker units.

A second aspect of the present invention will then be described.

The basic concept of the second aspect is as follows.

The problems of loudspeaker size reduction and its attendant degradationin bass frequency characteristics can be solved by isolating thediaphragm of the loudspeaker unit from any influence of damping whichmay be caused by the air spring lying within the enclosure.

For example, a stringed instrument such as a guitar or a contrabass canproduce excellent basses or low-frequency sounds under the action of itsresonance box although it merely has vibrating elements with minutesurface areas in the form of strings. It can also produce extremely richharmonics providing overtone components.

This is due to the fact that vibrations of the strings acting as thevibrating elements are transmitted via the bridges to the resonance boxso as to utilize the resonance of the body as much as possible.

As is apparent from this example, the enclosure can be used as theresonance box in order to achieve most simple and effective reproductionof basses by the loudspeaker system.

Thus, in the second aspect of the present invention, the outerperipheral site of the loudspeaker unit is provided with predeterminedair passages extending along substantially the overall inner perimeterof the baffle plate opening, for allowing a communication between theinterior and exterior of the enclosure, and the loudspeaker unit islocated apart from the opening, e.g., to such an extent as to prevent anoccurrence of degradation of bass frequency characteristics arising fromdetouring of the basses without any intimate contact with the baffleplate opening surface of the enclosure, to thereby obviate anyinfluences on the diaphragm of the air spring lying within the enclosureto consequently achieve an effective use of the enclosure as theresonance box.

The second aspect of the present invention aims for example to extendthe low-frequency characteristics and to improve the quality of soundsover the full ranges for a bass loudspeaker including a flame rib whichacts as the fitting surface to the baffle plate but has no even annularshape or including the fitting surface having a small area due to itssmall diameter, wherein it may be difficult to easily and securelyregulate the gaps formed along substantially the overall inner perimeterof the baffle plate opening between the rear face of the outerperipheral portion of the loudspeaker unit and the front face of thebaffle plate.

In the mid-frequency sound loudspeaker system and the high-frequencysound loudspeaker system, for the purpose of improving the auditorylocalization of image sounds through the radiation of sounds within theenclosure from the periphery thereof, a large-diameter annular rim ismounted on the rear face or front face of the outer peripheral portionof the loudspeaker unit so that confronting areas are increased of boththe rear face or the front face of the outer peripheral portion of theloudspeaker unit and the front face or the rear face of the baffleplate, thereby ensuring an appropriate resistance of air flowing throughthe gaps to prevent any degradation of the low-frequencycharacteristics.

Description will then be made of embodiments of the loudspeaker systembased on such a basic concept of the second aspect of the presentinvention.

FIG. 14 is a longitudinal sectional view of the loudspeaker system inaccordance with a first embodiment.

In this diagram, the loudspeaker system comprises an enclosure 110, aloudspeaker unit 113 for low-frequency sounds fitted to an opening 112in a baffle plate 111 situated at the front of the enclosure 110, and aloudspeaker unit 115 for high-frequency/mid-frequency sounds fitted toan opening 114.

The loudspeaker unit 113 for low-frequency sounds is mounted on thebaffle plate 111 in such a manner that gaps are formed between anannular rim 116 fitted to the rear face of a flange 113A at the outerperipheral portion of the loudspeaker unit 113 and the front face of thebaffle plate 111, the gaps providing predetermined air passages allowinga communication between the interior and the exterior of the enclosure110.

In this embodiment, a plurality of tubular spacers 117 are interposedbetween the internal face of an annular rim 116 on the rear face of theflange 113A at the outer peripheral portion of the loudspeaker unit 113for low-frequency sounds and the front face of the baffle plate 111 sothat the loudspeaker unit 113 for low-frequency sounds is secured to thebaffle plate 111 by means of machine screws 118 acting as fittings forinsertion into the spacers 117.

In this case, eight screw insertion holes are formed in equi-angularlyspaced manner in both the annular rim 116 on the flange 113A at theouter peripheral portion of the loudspeaker unit 113 for low-frequencysounds and in the perimeter of the opening in the baffle plate 111, themachine screws 118 being inserted through the insertion holes associatedwith the loudspeaker unit 113 for low-frequency sounds, through holes inthe annular rim 116, through holes in the spacers 15 and through theinsertion holes associated with the baffle plate 111 in the mentionedorder, after which nuts 119 are screwed and tightened onto ends,protruding from the rear face of the baffle plate 111, of threadedleading portions of the machine screws 118.

On the other hand, the unit 115 for high-frequency/mid-frequency soundsis mounted on the baffle plate 111 in such a manner that gaps are formedbetween an annular rim 120 fitted to the rear face of a flange 115A atthe outer peripheral portion of the unit 115 and the front face of thebaffle plate 111, the gaps providing predetermined air passages allowinga communication between the interior and the exterior of the enclosure110.

In this embodiment, a plurality of tubular spacers 121 are interposedbetween the internal face of an annular rim 120 on the rear face of theflange 113A at the outer peripheral portion of the loudspeaker unit 115for high-frequency/mid-frequency sounds and the front face of the baffleplate 111 so that the loudspeaker unit 115 forhigh-frequency/mid-frequency sounds is secured to the baffle plate 111by means of machine screws 122 acting as fittings for insertion into thespacers 121 and by means of nuts 123 mating therewith.

The spacers 117 and 121 for use herein can be made of, e.g., a rigidmaterial such as metals (vibration transmission type), or a resilientmaterial or member such as rubbers or coil springs (vibration absorptiontype).

It is preferred in case of the vibration absorption spacers that betweenthe nuts 119, 123 and the baffle plate 111 there intervene a washer madeof rubber or other resilient material.

In the diagram, reference numeral 124A denotes a bass reflex portprovided by a bass reflex duct 124.

FIG. 15 is a longitudinal sectional view of a loudspeaker system inaccordance with a second embodiment.

In this embodiment, the loudspeaker unit 125 is mounted in such a mannerthat there are formed gaps having a predetermined distance between theexternal face of the annular rim 126 situated on the front face of theflange 125A of the loudspeaker unit 125 and the rear face of the baffleplate 111.

That is, a plurality of spacers 127 are interposed between the annularrim 126 attached to the front face of the flange 125A of the loudspeakerunit 125 and the rear face of the baffle plate 111 so that theloudspeaker unit 125 is fitted to the baffle plate 111 by means ofmachine screws 128 inserted through the spacers 127 and by means of nuts129 mating therewith.

It will be understood that the spacers 117, 121 and 127 may be formedintegrally with the annular rims 116, 120 and 126 or with the baffleplate 111.

For example, the baffle plate 111 may previously have a plurality ofspacer portions formed integrally therewith so that the annular rims116, 120 and 126 associated with the loudspeaker units 113, 115 and 125can be attached to the spacer portions.

For this attachment, rivets or split pins can be used. Alternatively,use may be made of pins and C-rings fitted into the pins.

FIGS. 16(A) and 16(B) are a front elevational view and a sideelevational view, respectively, of a loudspeaker unit of a loudspeakersystem in accordance with a third embodiment.

In this embodiment, the loudspeaker unit generally designated at 130 isprovided integrally with an annular rim 131, with a plurality of spacerportions 132 projecting backward from the rear face of the annular rim131 and with a ring-like rib 133 located behind the rear face of theannular rim 131 for coupling the spacer portions 132 with one another,the rib 133 being fastened to the baffle plate front face by means ofmachine screws and nuts.

Although not shown, the annular rim associated with the loudspeaker unitmay be provided integrally with a plurality of spacer portionsprojecting forwardly from the front face of the annular rim, and with aring-like rib positioned in front of the front face of the annular rimfor coupling the spacer portions together, the rib being fastened to thebaffle plate rear face by means of machine screws and nuts.

According to the thus configured loudspeaker system, the outerperipheral site of the loudspeaker unit is provided with predeterminedair passages formed along substantially the overall inner perimeter ofthe opening in the baffle plate, the air passages allowing acommunication between the interior and exterior of the enclosure,whereby the following functions and effects are presented.

That is, the predetermined air passages allowing a communication betweenthe interior and exterior of the enclosure serve as sound holes whichthrough the bass reflex action radiate resonant sounds within theinterior of the enclosure to reinforce the bass frequencies.

Influences on the diaphragm of inertial vibrations of the air springlying within the enclosure are reduced and transient characteristicsover the full reproduction range are improved, with the result that afree, easy and gloomless sound quality is obtained.

Furthermore, since the air passages are formed along the outerperipheral site of the loudspeaker unit so as to extend alongsubstantially the overall inner perimeter of the opening in the baffleplate, air can flow in and out uniformly through the outer peripheralsite of the loudspeaker unit and the coned paper of the loudspeaker unitcan have a gentle curvature toward the air passages, with the resultthat resistance to which the coned paper may be subjected as a result ofa variation in the air pressure within the interior of the enclosure iseffectively reduced, achieving an effective improvement in the qualityof sounds.

In particular, since the air passages are formed in close vicinity tothe loudspeaker unit and along substantially the overall inner perimeterof the opening in the baffle plate, it is possible to enhance the bassfrequency characteristics as well as to prevent any turbulences ofcharacteristics at the other frequencies.

By the way, in cases where the air passages are not equi-angularlyarranged and are spaced from one another to a considerable extent, thereis a deficiency that although the bass frequency characteristics can bereinforced, the other frequencies may be subjected to any turbulences asset forth in connection with the prior art.

It has been found out that in the woofer unit or full-range unit, theoptimal value can be conferred on the spatial volume providedequi-angularly between the periphery of the woofer unit frame and thebaffle face by use of the spacers at the positions of the unit mountingscrews, whereby the optimal spatial volume can serve as a regulator tocontrol the air pressure within the enclosure. Furthermore, the qualityof sounds from the sound generator has been improved by fixing thevibration body to the baffle face at several points in place of thesurface of the vibration body.

It is thus possible to suppress any damping in the bass characteristicseven when the mounting volume is smaller than the enclosure volumerequired by the loudspeaker unit, whereupon a small-sized enclosure canbe used for the loudspeaker unit having a large-diameter diaphragmcapable of high-efficient and high-withstand input, therebysimultaneously achieving an improvement in efficiency and a reduction insize of the loudspeaker system.

In particular, by virtue of providing the rear face or front face of theouter peripheral portion of the loudspeaker unit with the annular rimfor regulating the confronting areas of the rear face or front face ofthat outer peripheral portion and of the front face or rear face of thebaffle plate, the following functions and effects are presented.

For a bass loudspeaker including a flame rib which acts as the fittingsurface to the baffle plate but has no even annular shape or including asmall fitting surface area wherein it may be difficult to regulate thegaps formed along substantially the overall inner perimeter of thebaffle plate opening between the rear face of the outer peripheralportion of the loudspeaker unit and the front face of the baffle plate,a large-diameter annular rim is mounted on the front face or rear faceof the outer peripheral portion of the loudspeaker unit so as toincrease the confronting areas of the rear face or front face of theouter peripheral portion and of the front face or rear face of thebaffle plate, whereby there can easily be achieved an enhancement in thelow-frequency characteristics and an improvement in the quality ofsounds over the full range.

That is, through any regulation of the area of the annular rim toregulate the volume of the gap lying between the baffle plate and theannular rim, control is provided of the mass of air passing through thegap and of the resistance upon the passage so as to ensure the optimumaction of the loudspeaker unit diaphragm, whereby the amount of airdischarge and intake is added to the additional mass of the diaphragm,thus presenting a function to lower the minimum resonance frequency.Simultaneously, air around the diaphragm is discharged and taken incircumferentially evenly and with an appropriate resistance whereuponthe force of the piston action exerted on the voice coil and itsvicinity can reach up to the periphery of the diaphragm in awell-balanced manner, thus preventing any possible abnormal diaphragmvibrations, lowering the enclosure stiffness, blocking rise of Q of thevoice coil, as well as providing effectively improved low frequencycharacteristics.

In the mid-frequency sound loudspeaker system and the high-frequencysound loudspeaker system, for the purpose of improving the auditorylocalization of image sounds through the radiation of sounds within theenclosure from the periphery thereof, a large-diameter annular rim ismounted on the rear face or front face of the outer peripheral portionof the loudspeaker unit so as to increase the confronting areas of boththe rear face or the front face of the outer peripheral portion of theloudspeaker unit and the front face or the rear face of the baffleplate, thereby making it possible to prevent the low-frequencycharacteristics from being degraded.

In other words, in the mid-frequency sound loudspeaker system and thehigh-frequency sound loudspeaker system, through the regulation of thevolume of the gap lying between the baffle plate and the annular rim, itis possible to prevent bass outputs of the entire loudspeaker systemfrom becoming lower by the actions of the mass of air passing throughthe gap and of the resistance upon the passage.

In such a case, for the purpose of ensuring a smooth air inflow andoutflow at the opening in the baffle plate, it is preferred in anyloudspeaker units for low-frequency sounds, mid-frequency sounds andhigh-frequency sounds to countersink the surface of the opening 112 inthe baffle 111 on the internal side of the enclosure 110 to aconsiderable extent (countersunk portion 112A) as in a fourth embodimentshown in FIG. 17 for example and to roundly chamfer the surfaceconfronting the outer peripheral portion of the loudspeaker unit 113,thereby obviating the function of rectification of air passing throughthe gap whose dimensions have been reduced as a result of the provisionof the annular rim 116, to consequently prevent the occurrence of anydistortions.

As described hereinabove, the addition of the annular rim enables thelength of the air passages to be adjusted in an appropriate mannerthrough the regulation of the gaps formed along substantially theoverall inner perimeter of the opening in the baffle plate between therear face of the outer peripheral portion of the loudspeaker unit andthe front face of the baffle plate, whereupon it is possible to suppressany reduction in the additional mass on the loudspeaker unit diaphragmarising from the internal air when the volume of the enclosure issmaller than the volume required by the woofer unit as well as tosuppress any damping in the bass reproduction characteristics. This willespecially be effective in the small-sized loudspeaker system in whichits additional mass on the loudspeaker unit diaphragm is liable to lowerand in which its bass reproduction characteristics are apt to damp.

The following advantages are presented by the embodiments which includegaps providing air passages and formed by the interposition of theplurality of spacers between the internal face of the annular rimassociated with the loudspeaker unit and the baffle plate front face orbetween the external face of the annular rim and the baffle plate rearface.

That is, the spacers can transmit vibrations of the loudspeaker unitframes to the baffle plate and act like the bridges of the contrabass,adding to the above resonance through the effective vibrations of theenclosure.

Also, depending on the design purposes, the spacers can be made ofmaterials such as rubber or other resins having a large vibrationabsorptivity or of materials such as metals having a small vibrationabsorptivity so as to provide a control of the resonance of the baffleplate.

Furthermore, it is possible to form air vents at the outer peripheralportion of the loudspeaker unit by simple modifications such as additionof the spacers, alterations of shape of the opening in the baffle plateand alterations of shape of the outer peripheral portion of theloudspeaker unit, thereby eliminating a need to impart uniquespecifications to the loudspeaker unit itself, allowing an easyapplication to the existing loudspeaker systems, and providingcost-efficient loudspeaker unit structure without causing anycomplication and any increase in weight.

As shown in the embodiment of FIG. 14, in case of providing a bassreflex port 124A by a bass reflex duct 124 or providing a bass radiationhole for bass reflex, it is possible to lower the lowest frequency bandas compared with the ordinary bass reflex type by imparting as low aresonance frequency as possible to the bass reflex ports or the bassradiation holes.

Furthermore, by employing the structure including the annular rim andspacers which are previously formed integrally with the loudspeaker unititself as in the embodiment of FIG. 16, the number of parts of theapparatus can totally be reduced. Application of the second aspect ofthe present invention to the loudspeaker system will thus becomepossible by the attachment of only the loudspeaker unit, contributing tofabrication easiness.

The above embodiments of the second aspect of the present invention areapplicable to loudspeaker systems provided in various types of acousticequipment, especially to loudspeaker systems for SR systems, domesticaudio loudspeaker systems, radio cassette players, sing-along machines,personal computers and television sets.

In the event of the loudspeaker units built into the wall surfaces orautomobile doors in particular, the loudspeaker units can be mounted onthe fitting portion (acting as the baffle plate) in accordance with themethods of the above embodiments.

Furthermore, in order to improve the external appearance, the openingsof the air passages toward the exterior may be covered with asound-permeable cloth or the like.

In case of aiming to reproduce a heavy low-frequency band, it is alsopossible to effectively extend the bass reproduction limit frequency byfurther adding resonance ducts or adding motional feedback or equalizeroperations to the loudspeaker systems including the loudspeaker unitsconfigured in accordance with the second aspect of the presentinvention.

The inventors have herein made experiments for comparing among aloudspeaker system A-1 of the second aspect based on the followingspecifications (use of the spacers with the annular rim), a conventionalloudspeaker system A-2 based on the following specifications (use ofonly the spacers) and a conventional loudspeaker system A-3 (no use ofthe spacers and annular rim) (see a characteristic diagram of FIG. 18showing the results of the experiments).

(Loudspeaker System Specifications)

A 13 cm dia. woofer unit (f_(o)=80 Hz) was mounted as the loudspeakerunit on a bass reflex type enclosure (inner dimensions: 26.7 cm(height)×16.4 cm (width)×17.3 cm (depth)) having an actual volume of 7.6lit. in a manner spaced apart by a predetermined distance Rh (0.11 mm)from the baffle plate by means of the spacers.

While hearing musical signals, the frequency characteristics andimpedance characteristics were measured to obtain the optimum value ofthe predetermined distance Rh.

Furthermore, a bass reflex duct providing F_(o′)=55.05 Hz was employedfrom calculations and experiments under ordinary bass reflex actions. Asa result, a 2.9 cm (i.d.)×7 cm pipe duct was mounted on the back of theenclosure. The interior sound absorption processing was merely done inthe form of adhesion of a rough felt of the order of 5 mm in thicknessto the inner bottom of the enclosure.

As is apparent from the characteristic diagram of FIG. 18, in theloudspeaker unit (A-1) in case of attachment of a 170 mm dia. 3 mm thickacrylic annular rim to the loudspeaker unit frames, the low-frequencyband from 10 Hz to 42 Hz had a higher output by 1 db than the bassreflex type loudspeaker system (A-3) in which the conventional unit wasmounted on the baffle in an intimate contact manner. If the loudspeakersystem has a 3 db lower reproduction efficiency, then double the outputof the power amplifier to be operated will be needed to acquire the samesound pressure. This will correspond to an improvement of the order of33% for the amplifier.

In case of the conventional loudspeaker system (A-2) having no annularrim, some frequency bands presented degraded bass characteristics ascompared with the loudspeaker system (A-3), although in case ofattachment of the annular rim, any bass output lower than theloudspeaker system (A-3) was not found over the low-frequency band from10 Hz to 42 Hz.

The conventional bass reflex type was unable to have such a low f_(0′)since the bass tended to show descending characteristics. In thisexperiments, however, improvements of +3 db and +4 db were found in thebands ranging from 15 Hz to 35 Hz and from 58 Hz to 79 Hz, respectively,with a lower f_(o′) being 55.05 Hz, as compared with the product off_(o′)=67 Hz which was designed under the same conditions by themanufacturer in accordance with the ordinary bass reflex type designmethod.

The inventors further made the following experiment.

In case of a two-way loudspeaker system in accordance with presentapplication (the same will apply to three-way and four-way loudspeakersystems), not only the woofer but also the tweeter needs to be lifted inorder to ensure good tone balances and natural feelings of sounds ofwaves or the like. Furthermore, with the tweeter lifted, sounds from thewoofer with in the enclosure had better be radiated from the peripheryof the tweeter in order to improve the auditory localization. For thisreason, the present applicant simply mounted the tweeter apart from thebaffle plate in the prior application.

However, this may possibly permit any leak of air from the periphery ofthe tweeter to impair the effect of the bass reflex duct, eventuallylowering the bass reproduction capacity of the loudspeaker system.

Thus, according to the result of the experiment on the configurationemploying the second aspect of the present invention, for example, onthe configuration in which the tweeter fitted to an 80 mm dia. 3 mmthick acrylic annular rim is threadedly mounted via spacers made of thinfilms (e.g., wraps) in a manner spaced apart from the baffle plate byabout 0.01 mm, it has turned out that similar sound effects are obtainedand any degradation in bass characteristics is prevented. Furthermore,peaks and valleys in the high-frequency characteristics were flattenedto obtain smoother characteristics.

The results of such experiment are shown in FIGS. 19 to 24 which arecharacteristic diagrams of two-way loudspeaker system complete models 1to 3 in accordance with the present application.

FIG. 19 is a characteristic diagram of a model B-1 using an 80 mm dia. 3mm thick acrylic annular rim so that the tweeter is mounted 0.01 mmapart from the baffle plate and using a 170 mm dia. 3 mm thick acrylicannular rim so that the woofer is mounted 0.11 mm apart from the baffleplate.

FIG. 20 is a characteristic diagram of a model B-2 using only theannular rim for the woofer but having the conventional loudspeaker unitin familiar contact with the baffle plate for the tweeter, whereinequivalent characteristics are secured in the low-frequency band withthe increased output and flattening in the high-frequency band ascompared with the characteristic of a model B-3 described later which issubjected in principle to no impairment of the bass reflex port effectsdue to the air leakage.

FIG. 21 is a characteristic diagram of the model B-3 using only theannular rim for the woofer but having no annular rim for the tweeter,with the loudspeaker unit being fitted via a 0.45 mm thick washer to thebaffle plate, and with the gap defined between the loudspeaker unit andthe baffle plate being set to a distance allowing tones of cymbals orthe like to become clearest as a result of hearing of a music, whereinthe low-frequency characteristics are degraded to a large extent (about3 db at maximum) as compared with the other models B-1 and B-2 due tothe air leakage from the periphery of the tweeter. With respect to thehigh-frequency sound output and flattening as well, it is inferior tothe model B-1. The presence of the effect of the annular rim for use inthe model B-1 attached to the tweeter will become more apparent alsofrom this model B-3 characteristics.

It will be appreciated that the characteristic diagram of FIG. 22 showsthe high-frequency characteristics of the models B-1 and B-3 in anenlarged scale for improvement in visibility, that the characteristicdiagram of FIG. 23 shows the high-frequency characteristics of the modelB-1 in an enlarged scale, and that the characteristic diagram of FIG. 24shows the high-frequency characteristic of the model B-3 in an enlargedscale.

INDUSTRIAL APPLICABILITY

According to the first aspect of the present invention as set forthhereinabove, by virtue of the configuration in which the predeterminedair passages are provided at the outer peripheral site of theloudspeaker unit in such a manner as to extend along substantially theoverall inner perimeter of the opening in the baffle plate, the airpassages serving to allow a communication between the interior andexterior of the enclosure, it is possible to provide a high soundquality loudspeaker system achieving an enhancement of the low-frequencyband, a reduction of distortions and a high efficiency whilesimultaneously reducing the size and weight of the enclosure, as well ashaving improved transient characteristics and economic considerations.

According to the second aspect of the present invention, by virtue ofthe simple configuration in which formation is made at the outerperipheral site of the loudspeaker unit in such a manner as to extendalong substantially the overall inner perimeter of the opening in thebaffle plate, it is possible to provide a high sound quality loudspeakersystem achieving an enhancement of the low-frequency band, reduction ofdistortions and a high efficiency while simultaneously reducing the sizeand weight of the enclosure, as well as having improved transientcharacteristics and economic considerations. In particular, the rearface of the outer peripheral portion of the loudspeaker unit is providedwith the annular rim for regulating the area confronting both the rearsurface of the outer peripheral portion and the front face of the baffleplate whereby the gap is regulated which is defined between the rearface of the outer peripheral portion of the loudspeaker unit and thefront face of the baffle plate and which extends along substantially theoverall inner perimeter of the opening in the baffle plate, toconsequently enable the length of the air passages to be regulated. Itis thus possible to suppress any reduction in the additional mass on theloudspeaker unit diaphragm arising from the enclosure interior air andto suppress any damping in the bass reproduction characteristics.Particular effectiveness will therefore be imparted to any small-sizedloudspeaker systems liable to suffer any reduction in additional mass onthe loudspeaker unit diaphragm and apt to undergo any damping in thebass reproduction characteristics.

What is claimed is:
 1. A loudspeaker system including an enclosure and aloudspeaker unit adapted to be fitted to an opening in a baffle plate atthe front of said enclosure, wherein said loudspeaker unit is mountedvia a plurality of spacers on said baffle plate in such a manner thatgaps are formed as predetermined air passages between the rear face ofthe outer peripheral portion of said loudspeaker unit and the front faceof said baffle plate or between the front face of the outer peripheralportion of said loudspeaker unit and the rear face of said baffle plate,said predetermined air passages extending along substantially theoverall inner perimeter of said opening in said baffle, for allowing acommunication between the interior and exterior of said enclosure,wherein said plurality of spacers are each in the form of asubstantially tubular member, with fittings inserted through theinterior of said tubular member being securely fastened to the outerperipheral portion of said loudspeaker unit and to said baffle plate. 2.A loudspeaker system according to claim 1, wherein said plurality ofspacers are each formed of a material having a predetermined vibrationabsorptivity.
 3. A loudspeaker system including an enclosure and aloudspeaker unit adapted to be fitted to an opening in a baffle plate atthe front of said enclosure, wherein said loudspeaker unit is mountedvia a plurality of spacers on said baffle plate in such a manner thatgaps are formed as predetermined air passages between the rear face ofthe outer peripheral portion of said loudspeaker unit and the front faceof said baffle plate or between the front face of the outer peripheralportion of said loudspeaker unit and the rear face of said baffle plate,said predetermined air passages extending along substantially theoverall inner perimeter of said opening in said baffle, for allowing acommunication between the interior and exterior of said enclosure,wherein said loudspeaker unit is provided at its outer peripheralportion with a plurality of spacer portions projecting backward from therear face of said outer peripheral portion and an annular rib portionlocated behind the rear face of said outer peripheral portion of saidloudspeaker unit for coupling said spacer portions to one another, saidspacer portions and said rib portion being formed integrally with saidouter peripheral portion of said loudspeaker unit, said rib portionbeing fitted to the front face of said baffle plate so as to form saidplurality of gaps.
 4. A loudspeaker system including an enclosure and aloudspeaker unit adapted to be fitted to an opening in a baffle plate atthe front of said enclosure, wherein said loudspeaker unit is mountedvia a plurality of spacers on said baffle plate in such a manner thatgaps are formed as predetermined air passages between the rear face ofthe outer peripheral portion of said loudspeaker unit and the front faceof said baffle plate or between the front face of the outer peripheralportion of said loudspeaker unit and the rear face of said baffle plate,said predetermined air passages extending along substantially theoverall inner perimeter of said opening in said baffle, for allowing acommunication between the interior and exterior of said enclosure,wherein a plurality of rib portions are formed as spacers integrallyaround said opening in said baffle plate, said rib portions havinggrooves formed in their respective inner peripheral faces, saidloudspeaker unit having a plurality of outwardly extending attachmentprotrusions formed on its outer peripheral portion, said attachmentprotrusions being fitted into said grooves in said rib portions byturning said loudspeaker unit, to thereby form said gaps.
 5. Aloudspeaker system including an enclosure and a loudspeaker unit adaptedto be fitted to an opening in a baffle plate at the front of saidenclosure, wherein said loudspeaker unit is mounted on said baffle platein such a manner that between the rear face of the outer peripheralportion of said loudspeaker unit and the front face of said baffle platethere are formed gaps acting as predetermined air passages which extendalong substantially the overall inner perimeter of said opening in saidbaffle plate and which allow a communication between the interior andexterior of said enclosure, and wherein said loudspeaker unit has on itsouter peripheral portion rear face an annular rim for adjustingconfronting areas of the rear face of said outer peripheral portion andof the front face of said baffle plate, wherein a plurality of spacerportions projecting backward from the rear face of said annular rimportion, and an annular rib portion positioned behind the rear face ofsaid annular rim portion for coupling said plurality of spacers to oneanother, said rim portion, said plurality of spacer portions and saidrib portion being integrally formed with said outer peripheral portionof said loudspeaker unit, said rib portion being fitted to the frontface of said baffle plate.
 6. A loudspeaker system including anenclosure and a loudspeaker unit adapted to be fitted to an opening in abaffle plate at the front of said enclosure, wherein said loudspeakerunit is mounted on said baffle plate in such a manner that between thefront face of the outer peripheral portion of said loudspeaker unit andthe rear face of said baffle plate there are formed gaps acting aspredetermined air passages which extend along substantially the overallinner perimeter of said opening in said baffle plate and which allow acommunication between the interior and exterior of said enclosure, andwherein said loudspeaker unit has on its outer peripheral portion frontface an annular rim for adjusting confronting areas of the front face ofsaid outer peripheral portion and of the rear face of said baffle plate,wherein a plurality of spacer portions projecting forward from the frontface of said annular rim portion, and an annular rib portion positionedin front of the front face of said annular rim portion for coupling saidplurality of spacers to one another, said rim portion, said plurality ofspacer portions and said rib portion being integrally formed with saidouter peripheral portion of said loudspeaker unit, said rib portionbeing fitted to the rear face of said baffle plate.